Bomb physicists at the nation’s two nuclear explosives labs have delivered preliminary designs to the Bush administration as potential replacements for the most numerous warheads in the U.S. nuclear arsenal.

Two teams of designers at Lawrence Livermore and Los Alamos labs, both run by the University of California, have swapped their proposed replacements for the 100-kiloton thermonuclear warheads riding on U.S. submarine-launched missiles and, according to a recent administration report, possibly for warheads on silo-based missiles as well.

The teams are poring over details of each other’s bombs as a matter of scientific peer review and a step in the head-to-head competition to see which lab’s bomb, if any, will be built.

In a recent report to Congress, Defense Secretary Donald Rumsfeld and Energy Secretary Samuel Bodman say the administration is on track to finish a feasibility study of the “reliable replacement warhead” program by November and choose a design.

Production of the first new warheads is set for 2012, and the study suggests that as much as the entire U.S. nuclear arsenal could be replaced by new bombs by 2035.

The notion of building a new U.S. arsenal is controversial.

Designing and making new H-bombs while maintaining thousands of existing weapons is expected to be costly. The Rumsfeld-Bodman report says that “cost estimates for the RRW program have not yet been developed,” but the program “has the potential to reduce comparative life cycle costs” by designing weapons that are cheaper and easier to manufacture.

The existing arsenal of seven basic types of missile warheads and air-dropped bombs were fielded after a combined total of 150 nuclear explosive tests. They are H-bombs that evolved through decades into highly sophisticated devices with nearly as many parts as a commercial jet airliner yet shoehorned into small packages to squeeze the most destructive power out of the least size and weight.

In doing so, scientists and engineers used toxic metals, adhesives and plastics from the 1960s and’70s that administration weapons officials say are increasingly difficult and costly to use today as U.S. weapons workers replace aging parts.

The Rumsfeld-Bodman report says that chiefs of the nation’s weapons labs, as well as officers and commanders in the Pentagon and Strategic Command, worry that the weapons are becoming less safe and reliable.

As insurance, the report says, the United States is storing thousands of nuclear explosives in reserve, ready in case of breakdown in any of the fielded bombs or warheads.

Critics say the existing arsenal is healthy and extremely capable, and the chiefs of the weapons labs have certified the health of every bomb and warhead type to the two secretaries and the president every year for a decade. Designing new warheads without testing them, critics say, is risky and counterproductive to U.S. efforts at discouraging other nations from building nuclear arms.

“There is a motive behind this that has nothing to do with the health of the stockpile. I suggest that the motive is budget,” said Bob Peurifoy, a former Sandia National Laboratories weapons executive.

He said weapons workers know the existing arsenal well and can remanufacture its parts precisely.

“But that’s no fun. The fun for some of these folks is to go out and try to design new things,” he said. “I believe it’s more important to put attention to the national security needs of the country than to allow them to have their fun. It comes down to a question: Do the (weapons design) labs work for the country, or does the country work for the labs?”

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